Probe

ABSTRACT

An acoustic wave detector that detects an acoustic wave from a subject, an optical fiber that guides light emitted from a light source to a probe body, and a light guide member that guides light from a light entrance end, which is optically coupled to the optical fiber, to a light exit end, which is located in the vicinity of the acoustic wave detector, are provided. The light guide member is secured in the probe body with a securing material provided at least partially around the light guide member. The conditional expression below is satisfied: 
       sin −1 ( n 2/ n 1)×(180°/π)&lt;90°−θ i  
 
     where n1 is a refractive index of the light guide member, n2 is a refractive index of the securing material, and θi is a spread angle of incoming light from the optical fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT International Application No.PCT/JP2013/000523 filed on Jan. 31, 2013, which claims priority under 35U.S.C §119 (a) to Japanese Patent Application No. 2012-021670 filed onFeb. 3, 2012 and Japanese Patent Application No. 2013-011039 filed onJan. 24, 2013. Each of the above applications is hereby expresslyincorporated by reference, in its entirety, into the presentapplication.

TECHNICAL FIELD

The present invention relates to a probe, and more particularly to aprobe used in photoacoustic imaging.

BACKGROUND ART

Ultrasonography is known as one of imaging examination methods thatallow non-invasive examination of the state of the interior of a livingbody. In ultrasonography, an ultrasound probe that can transmit andreceive ultrasound is used. Ultrasound transmitted from the ultrasoundprobe to the subject (living body) travels through the interior of theliving body and is reflected at a tissue interface. Then, the reflectedultrasound is received by the ultrasound probe. Based on the time takenfor the reflected ultrasound to return to the ultrasound probe, thedistance is calculated, thereby imaging the state of the interior.

Further, photoacoustic imaging, which images the interior of a livingbody using the photoacoustic effect, is known. In photoacoustic imaging,in general, pulsed laser light, for example, is applied to the interiorof a living body. In the interior of the living body, a living tissueabsorbs energy of the pulsed laser light and ultrasound (a photoacousticsignal) is generated due to adiabatic expansion caused by the energy.This photoacoustic signal is detected using an ultrasound probe, or thelike, and a photoacoustic image is constructed based on the detectedsignal, thereby visualizing the interior of the living body based on thephotoacoustic signal.

Usually, in a ultrasound probe, the interior of the probe body is filledwith a potting agent to secure parts contained in the probe body.Potting the interior of the probe body is taught, for example, inJapanese Unexamined Patent Publication Nos. 7(1995)-313507 and8(1996)-010255 (hereinafter, Patent Documents 1 and 2). As the pottingagent, an epoxy resin, etc., may be used, for example.

In the photoacoustic imaging, light from a laser light source may beguided to the ultrasound probe using an optical fiber, or the like, toapply the laser light from the ultrasound probe. An ultrasound probeincluding a light application section is taught in Japanese UnexaminedPatent Publication No. 2008-49063 (hereinafter, Patent Document 3), forexample. Patent Document 3 teaches that the end portion of the opticalfiber on the light exit end side is disposed adjacent to ultrasoundtransducers and secured integrally with the ultrasound transducers. Thelight exit end of the optical fiber is secured in a hole provided in aholder such that the light is applied in a direction in which ultrasoundfrom the ultrasound transducers travels.

DISCLOSURE OF INVENTION

As an ultrasound probe including a light application section, anultrasound probe that includes light guide plates in a probe body,wherein light guided using optical fibers, or the like, is inputted tothe light guide plates and the light is outputted toward the subjectfrom light exit faces of the light guide plates, is considered. Thelight guide plates may be made of quartz glass, for example. The probebody of the above-described ultrasound probe is filled with a resin,such as an epoxy resin, to secure component parts, including the lightguide plates, contained in the probe body. At this time, if acommonly-used potting agent is used to secure the light guide plates,there is only a small refractive index difference between the lightguide plates and the potting agent and the light in the light guideplates may not be reflected in the light guide plates, causing lightleakage.

More specifically, a typical optical fiber has a numerical aperture ofNA=0.23, and a spread angle θi of the outgoing light is around 13.3°(θi=sin⁻¹(NA)). A standard refractive index of a commonly-used pottingagent, such as an epoxy agent, is in the range from 1.42 to 1.45. In thecase where the light guide plates are made of quartz, the refractiveindex of the light guide plates is 1.45 for light having a wavelength inthe range from 700 nun to 800 nm. When the light from the optical fiberis normally incident on the light entrance side of each light guideplate having a rectangular solid shape, the light outputted from theoptical fiber has the spread angle θi, and the maximum incidence angleof the outgoing light from the optical fiber incident on the interfacebetween the light guide plate and the potting agent is 90°−θi=76.7°.

In a case where the potting agent has a refractive index of 1.42, thecritical angle (the smallest incidence angle for total reflection) atthe interface between the light guide plate and the potting agent is78.3°. In a case where the potting agent has a refractive index of 1.45,the critical angle at the interface between the light guide plate andthe potting agent is 90°. In these cases, the light from the opticalfiber enters the interface between the light guide plate and the pottingagent at an angle smaller than the critical angle. Therefore, part ofthe light travelling through the light guide plate is not reflected atthe interface between the light guide plate and the potting agent,causing light leakage.

In view of the above-described circumstances, the present invention isdirected to providing a probe that can prevent light leakage from lightguide plates that are secured in a probe body with a potting agent.

In order to accomplish the above-described object, the inventionprovides a probe comprising: an acoustic wave detector that detects atleast an acoustic wave from the subject; an optical fiber that guideslight emitted from a light source to a probe body; and light guide meansthat guides light from a light entrance end to a light exit end, thelight entrance end being optically coupled to the optical fiber and thelight exit end being located in the vicinity of the acoustic wavedetector, wherein the light guide means is secured in the probe bodywith a securing material provided at least partially around the lightguide means, and the conditional expression below is satisfied:

sin⁻¹(n2/n1)×(180°/π)<90°−θi

where n1 is a refractive index of the light guide means, n2 is arefractive index of the securing material, and θi is a spread angle oflight entering the light entrance end from the optical fiber.

In the invention, the light guide means may at least partially be madeof glass.

As the securing material, a fluorine resin material may be used.Specifically, tetrafluoroethylene-perfluorodioxole copolymer (T1E/PDD)may be used as the securing material.

Alternatively, a fluorosilicone rubber may be used as the securingmaterial. Still alternatively, a low-refractive index silicone resin ora methyl silicone resin having a refractive index lower than therefractive index of the light guide means may be used as the securingmaterial.

In the invention, the light exit end of the light guide means may becovered with the securing material.

The light guide means may comprise a first light guide member thatguides light emitted from the light source, and a second light guidemember that diffuses and guides the light guided by the first lightguide member to the vicinity of the acoustic wave detector.

In this case, the second light guide member may comprise a lightdiffusing member that diffuses incoming light, the light diffusingmember being disposed on the side where light from the first light guidemember enters.

It is preferred that the conditional expression below be satisfied:

sin⁻¹(n2/n3)×(180°/π)<90°−θd(where θd=(θi ²+θ1²)^(1/2)),

where n3 is a refractive index of the second light guide member, and θ1is a diffusion angle of the light diffusing member.

At least the second light guide member of the first and second lightguide members may be secured with the securing material. Alternatively,only the second light guide member of the first and second light guidemembers may be secured with the securing material.

In the invention, a structure where the securing material is provided toextend over a side surface of the light guide means between the lightentrance end and the light exit end may be adopted.

Alternatively, the securing material may be provided to extend over aside surface of the light guide means between the light exit end and aposition away from the light exit end by a predetermined distance. Inthis case, it is preferred that the predetermined distance be not morethan ⅓ of a distance between the light entrance end and the light exitend of the light guide means.

The securing material may be provided between the light guide means anda case forming the probe body or a case provided in the probe body.

The light guide means may be secured with the securing member between acase forming the probe body or a case provided in the probe body and aholding member that holds the acoustic wave detector. In this case, theacoustic wave detector may be attached to the holding member after thelight guide member is secured with the securing member.

The invention also provides a probe comprising: an acoustic wavedetector that detects at least an acoustic wave from the subject;

an optical fiber that guides light emitted from a light source to aprobe body; and light guide means that guides light from a lightentrance end to a light exit end, the light entrance end being opticallycoupled to the optical fiber and the light exit end being located in thevicinity of the acoustic wave detector, wherein the light guide means issecured in the probe body with a securing material provided at leastpartially around the light guide means between the light entrance endand a position away from the light entrance end by a distance h, whereinh=d/tan(θi), where d is a distance from a position where the opticalfiber is coupled to the light entrance end to a side surface of thelight guide means, and θi is a spread angle of light entering the lightentrance end from the optical fiber.

The above-described probe may have a structure where an area of the sidesurface other than an area corresponding to the distance h from thelight entrance end of the light guide means is covered with a layer ofair.

In the probe of the invention, a securing material having a lowrefractive index is used as the securing material that is used to securethe light guide means in the probe body. By using a securing materialthat is selected such that the critical angle for total reflection atthe interface between the light guide means and the securing materialbecomes smaller than the maximum incidence angle at which the lightentering the light guide means from the optical fiber enters theinterface between the light guide means and the securing material, lightleakage from the light guide means to the securing material can beprevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a photoacoustic diagnosticimaging system including a probe according to a first embodiment of theinvention,

FIG. 2 is a sectional view showing a cross section in the side surfacedirection of the probe,

FIG. 3 is a sectional view showing a cross section in the side surfacedirection of a probe of a comparative example,

FIG. 4 is a sectional view showing a cross section in the side surfacedirection of a probe according to a modification of the invention,

FIG. 5 is a sectional view showing a cross section in the side surfacedirection of a probe according to a second embodiment of the invention,

FIG. 6 is a sectional view showing a cross section of a part near thetip of a probe according to a third embodiment of the invention,

FIG. 7 is a sectional view showing a cross section of a part near thetip of a probe according to a fourth embodiment of the invention,

FIG. 8 is a sectional view showing a cross section of a part near thetip of a probe according to a fifth embodiment of the invention, and

FIG. 9 is a sectional view showing a cross section of a part near thetip of a probe according to a sixth embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings. FIG. 1 shows a photoacousticdiagnostic imaging system including a probe according to a firstembodiment of the invention. The photoacoustic diagnostic imaging systemincludes a probe 10, a light source unit 31, and an ultrasound unit 32.The probe 10 includes a light application section that applies light tothe subject, and an acoustic wave detector that is capable of detectingan acoustic wave (ultrasound, for example) at least from the subject.The acoustic wave detector includes a plurality of ultrasoundtransducers, which are one-dimensionally arranged, for example.

The light source unit 31 is a laser unit that generates a pulsed laserlight, for example, and generates light to be applied to the subjectfrom the probe 10. The probe 10 is connected to the light source unit 31via optical wiring 21. The optical wiring 21 is formed by a fiber bundleof several tens of optical fibers, for example. The pulsed laser lightgenerated at the light source unit 31 is guided by the optical wiring 21to the probe 10, and is applied to the subject from the lightapplication section of the probe 10.

The ultrasound unit 32 generates a photoacoustic image based on adetection signal (ultrasound signal) of an acoustic wave detected by theprobe 10. The probe 10 is connected to the ultrasound unit 32 viaelectric wiring 22. The ultrasound signal detected by the probe 10 istransmitted to the ultrasound unit 32 via the electric wiring 22 and isprocessed by the ultrasound unit 32.

FIG. 2 shows a cross section in the side surface direction of the probe10 viewed from a direction perpendicular to a direction in which theultrasound transducers are arranged. The probe 10 includes electronicmaterials 11, optical fibers 13, and light guide plates 14. Theelectronic materials 11 includes ultrasound transducers 12 forming anacoustic wave detector. The ultrasound transducers 12 detect ultrasoundat least from the subject. The electronic materials 11 may include,besides the ultrasound transducers 12, a pre-amplifier for amplifyingthe detected ultrasound, etc., for example.

The optical fibers 13 corresponds to the optical wiring 21 shown in FIG.1, and guide light emitted from the laser light source unit 31 (FIG. 1)to the probe body. The light guide plates 14 are light guide means, eachof which guides light from a light entrance end optically coupled to theoptical fiber 13 to a light exit end located in the vicinity of theultrasound transducers 12. Each optical fiber 13 is optically coupled,for example, to the center position of each light guide plate 14 in thelateral direction (x-direction) in the cross section shown in FIG. 2.The probe 10 includes at least two light guide plates 14, for example,and the two light guide plates 14 are disposed to face each other andsandwich the ultrasound transducers 12. The light guide plates 14 aremade of a glass material, for example.

The light guide plates 14 are secured in the probe body by a securingmaterial that is provided at least partially around the light guideplates 14. The securing material maybe made of a resin material, forexample. The light guide plates 14 are secured in the probe body by aresin 16 that fills a space between a case forming the probe body andthe electronic materials 11, for example. The resin 16 is provided toextend over the entire side surfaces (the entire surfaces in they-direction) between the light entrance ends and the light exit ends ofthe light guide plates 14, for example.

As the resin 16, a resin material having a lower refractive index thanthat of an epoxy resin, which is a commonly-used potting agent, is used.For example, a fluorine resin material is used as the resin 16.Specifically, tetrafluoroethylene-perfluorodioxole copolymer (TFE/PDD)can be used as the resin 16. Alternatively, a low-refractive indexsilicone resin (having a refractive index of 1.39) or a methyl siliconeresin (having a refractive index of 1.41) may be used as the resin 16.Still alternatively, in place of these resins, a fluorosilicone rubber(FE-123 having a refractive index of around 1.39, available fromShin-Etsu Chemical Co., Ltd.) may be used as the securing material.

Light entering the light entrance side of each light guide plate 14 fromthe end face of the optical fiber 13 travels through the light guideplate 14 with spreading at a spread angle θi depending on the numericalaperture NA of the end face of the optical fiber 13. When the light fromthe optical fiber 13 enters the light entrance side of the light guideplate 14 in the normal direction, the maximum incidence angle of thelight outputted from the optical fiber 13 and incident on the interfacebetween the light guide plate 14 and the resin 16 is 90°−θi. On theother hand, the critical angle (the smallest incidence angle for totalreflection) is sin⁻¹(n2/n1)×(180°/π), where n1 is a refractive index ofthe light guide plate 14, and n2 is a refractive index of the resin 16.When the critical angle is smaller than the maximum incidence angle onthe interface between the light guide plate 14 and the resin 16, thelight entering the light guide plate 14 travels toward the light exitend with being totally reflected.

A typical optical fiber has a numerical aperture of NA=0.23, and aspread angle θi of the outgoing light is around 13.3°. In a case wherethe light guide plates 14 are made of quartz, the light guide plates hasa refractive index of 1.45. As the resin 16, a fluorine resin having arefractive index n2=1.32 is used, for example. In this case, thecritical angle is 65.6°. This critical angle is smaller than the maximumincidence angle of 90°−13.3°=76.7° at the interface between the lightguide plate 14 and the resin 16, and therefore the light entering thelight guide plate 14 from the optical fiber 13 is totally reflected atthe interface between the light guide plate 14 and the resin 16.

In this embodiment, the light guide plates 14 are secured using theresin 16 having a low refractive index such that the critical angle fortotal reflection becomes smaller than the maximum incidence angle of thelight entering the interface between each light guide plate 14 and theresin 16. Namely, a resin material having a refractive index n2 thatsatisfies sin⁻(n2/n1)×(180°/π)<90°−θi is provided around the light guideplates 14 to secure the light guide plates 14. By using the resinmaterial that makes the critical angle for total reflection smaller thanthe maximum incidence angle at which the light outputted from theoptical fiber 13 enters the interface between each light guide plate 14and the resin 16, light leakage from the light guide plates 14 can beprevented. By preventing the light leakage, light entering the lightguide plates 14 can be efficiently guided to the light exit ends,thereby preventing decrease of intensity of light applied to thesubject.

As a comparative example, a case where the light guide plates 14 aresecured using a commonly-used potting agent is considered. FIG. 3 showsa cross section in the side surface direction of a probe of thecomparative example. Light guide plates 52 are optically coupled to theoptical fibers 51 to guide incoming light from the optical fibers 51toward the subject. In the case where the light guide plates 52 aresecured using, as the resin 53, an epoxy resin, which is a commonly-usedpotting agent and has a refractive index of around 1.42 to 1.45, thecritical angle is around 78.3° to 90°. In this case, the critical angleis greater than the maximum incidence angle at the interface betweeneach light guide plate 52 and the resin 53, resulting in light leakage.In order to prevent the light leakage, one may consider coating theinterface between each light guide plate 52 and the resin 53 with areflective film 54; however, this results in increase of the productionsteps and the production cost. In contrast, the embodiment of theinvention can prevent the light leakage without need of a reflectivecoating, and thus can minimize cost increase.

It should be noted that the resin 16 may not necessarily be provided toextend over the entire side surfaces between the light entrance ends andthe light exit ends of the light guide plates 14, and may be provided topartially extend over the side surfaces of the light guide plates 14.FIG. 4 shows a cross section in the side surface direction of amodification of the probe 10. In this example, the resin 16 is providedto extend only over the side surfaces of the light guide plates 14between the light exit ends of the light guide plates 14 and a positionaway from the light exit ends by a predetermined distance. For example,the resin 16 is provided to extend over a length not greater than ½, ordesirably not greater than ⅓ of the length from the light entrance endsto the light exit ends of the light guide plates 14. In this case, anecessary amount of the resin material can be reduced, although thestrength for securing the light guide plates 14 decreases.

Next, a second embodiment of the invention is described. FIG. 5 shows across section in the side surface direction of a probe according to asecond embodiment of the invention. In this embodiment, the light guideplates 14 are secured in the probe body by providing a resin 17 as thesecuring material at least partially around the light guide plates 14between the light entrance ends of the light guide plates 14 and aposition away from the light entrance ends by a predetermined distanceh. The side surfaces of the light guide plates 14 other than the areasbetween the light entrance ends and the position away from the lightentrance ends by the predetermined distance h are covered with a layerof air, for example.

For example, assuming that the thickness of each light guide plate 14 inthe lateral direction (x-direction) of the drawing is 2×d, each opticalfiber 13 is coupled to the center of each light guide plate 14 in thex-direction, and the spread angle of the light outputted from eachoptical fiber 13 is θi, then, light that has entered each light guideplate 14 enters the side surface (the side surface in the x-direction)of the light guide plate 14 at a position at a distance d/tan(θi) fromthe light entrance end. In other words, at an area between the lightentrance end and the position at the distance d/tan(θi) from the lightentrance end, no light outputted from the optical fiber 13 directlyenters the side surface of the light guide plate 14. In this embodiment,the resin 17 is provided to extend over that area. Namely, the resin 17is provided to extend over the area corresponding to h=d/tan(θi).

In this embodiment, the resin 17 is provided at least partially aroundthe light guide plates 14 between the light entrance ends of the lightguide plates 14 and the position away from the light entrance ends bythe predetermined distance h to secure the light guide plates 14 in theprobe body. By providing the resin 17 between the light entrance endsand the position at the predetermined distance defined by h=d/tan(θi) tosecure the light guide plates 14, light outputted from the optical fiber13 and entering the light guide plates 14 can be prevented from leakingout from the light guide plates 14. In this embodiment, the lightoutputted from the optical fiber 13 does not directly enter the resin17. Therefore, unlike the first embodiment, it is not necessary to use alow-refractive index resin material as the resin 17. Since the areas ofthe light guide plates 14 that do not correspond to the predetermineddistance h is covered with a layer of air, the refractive index is evensmaller than the case where a fluorine resin is used, and light enteringthe interface between each light guide plate 14 and the layer of air istotally reflected.

Next, a third embodiment of the invention is described. FIG. 6 shows across section of a part near the tip (on the ultrasound transducersside) of a probe according to the third embodiment of the invention. Inthis embodiment, a holding member 18 that holds the ultrasoundtransducers 12, which form the acoustic wave detector, is provided inthe probe. The holding member 18 may be formed integrally with a case15, which forms the outer covering, or may be formed separately from thecase 15. The light guide plates 14 are secured between the case 15 andthe holding member 18 with the resin 16 forming the securing member. Asthe resin 16, those described with respect to the first embodiment canbe used.

During assembly of the probe, the resin 16 in the hot state, forexample, is poured between the light guide plates 14 and the case 15 andthe holding member 18, and then is hardened to secure the light guideplates 14. Thereafter, the ultrasound transducers 12 are bonded to theholding member 18. As shown in FIG. 2, in the case where the light guideplates 14 are secured between the case and the electronic materials 11including the ultrasound transducers 12, the electronic materials 11 andthe ultrasound transducers 12 are exposed to heat from the resin 16 inthe hot state. In contrast, in this embodiment, the ultrasoundtransducers 12 can be attached to the holding member 18 after the lightguide plates are secured with the resin 16. Thus, the situation wherethe ultrasound transducers 12, which are weak against heat, are exposedto the heat from the resin 16 in the hot state can be avoided. Thisallows using a material that hardens at a higher temperature as thesecuring material for securing the light guide plates 14. Other effectsare the same as those of the first embodiment.

Next, a fourth embodiment of the invention is described. FIG. 7 shows across section of a part near the tip of a probe according to the fourthembodiment of the invention. In this embodiment, each light guide plate14 a includes a first light guide member 141 and a second light guidemember 143. The second light guide member 143 diffuses light guided bythe first light guide member 141 and guides the light to the vicinity ofthe ultrasound transducers 12. A gap of around 0.1 mm to 1 mm, forexample, is provided between the first light guide member 141 and thesecond light guide member 143. The resin 16 serving as the securingmember secures (parts of) the first light guide members 141 and thesecond light guide members 143 in the probe body.

The first light guide members 141 are made of glass, for example.High-energy laser from the light source enters the first light guidemembers 141, and the light entering the first light guide members 141spreads while being guided toward the second light guide members 143.Each second light guide member 143 includes, for example, glass and adiffuser plate (light diffusing member) 142, which is disposed at theend face of the glass facing the first light guide member 141. As thediffuser plate 142, a holographic diffuser can be used, for example. Thedivergence angle of the diverging light entering the second light guidemember 143 is further increased by the diffuser plate 142, and thediverging light is guided to the vicinity of the ultrasound transducers12. Specifically, the divergence angle of the light is increased toθd=(θi²+θ1²)^(1/2), where θ1 is a diffusion angle of the diffuser plate142.

In this embodiment, each first light guide member 141 is made oftransparent glass for receiving the incoming high-energy density laserlight outputted from the optical fiber 13 (FIG. 2), and the incominglight spreads while being guided through the transparent glass. Eachsecond light guide member 143 includes the diffuser plate 142 disposedon the light entrance side of transparent glass to further spread theincoming light from the first light guide member 141, and guides thelight toward the subject. This allows minimizing a difference of lightintensity between the central area and the peripheral area of the lightoutputted toward the subject.

In this embodiment, the light guide plates 14 a are secured by providinga resin material having a refractive index n2 that satisfiessin⁻¹(n2/n1)×(180°/π)<90°−θi around the light guide plates 14 a, therebyminimizing or eliminating leakage of light from the first light guidemembers 141. In particular, in a case where sin⁻¹(n2/n3)×(180°/π)<90°−θdis satisfied, where n3 is a refractive index of the second light guidemembers 143, leakage of light from the second light guide members 143can be minimized or eliminated.

Next, a fifth embodiment of the invention is described. FIG. 8 shows across section of a tip part of a probe according to the fifth embodimentof the invention. In the above-described fourth embodiment, both thefirst light guide members 141 and the second light guide members 143 aresecured in the probe body with the resin 16. In contrast, in thisembodiment, only the second light guide members 143 of the first andsecond light guide members 141 and 143 are secured with the resin 16. Inthis embodiment, it is preferred that sin⁻¹(n2/n3)×(180°/π)<90°−θd(where θd=(θi²+θ1²)^(1/2)) be satisfied, where n3 is a refractive indexof the second light guide members 143, and θ1 is a diffusion angle ofthe diffuser plates 142.

In this embodiment, only the second light guide members 143 of the firstand second light guide members 141 and 143 are secured with the resin 16in the probe body. This structure allows removing only the first lightguide members 141 of the first and second light guide members 141 and143 forming the light guide plates 14 a from the probe body, therebyallowing cleaning or replacement of the first light guide members 141.Further, in a case where the end faces of the second light guide members143 on the diffuser plates 142 side are exposed above the resin 16,cleaning or replacement of the diffuser plates 142 can be performed.Other effects are the same as those of the fourth embodiment.

Next, a sixth embodiment of the invention is described. FIG. 9 shows across section of a part near the tip of a probe according to the sixthembodiment of the invention. The probe of this embodiment differs fromthe probe of the first embodiment in that the light exit ends of thelight guide plates 14 are covered with the resin 16 forming the securingmaterial. Other features are the same as those of the first embodiment.

In a case where light from the light guide plates 14 are directlyapplied to a living body which is the subject, a difference between therefractive index of the living body and the refractive index of thelight guide plates 14 may hinder efficient application of the light tothe living body. In this embodiment, light outputted from the lightguide plates 14 is applied to the living body via the resin 16, whichreduces the difference between the refractive index of the living bodyand the refractive index of the glass, thereby allowing efficientapplication of the light to the living body. Other effects are the sameas those of the first embodiment.

It should be noted that, although the resin 16 for securing the lightguide plates 14 is provided between the case 15 forming the probe bodyand the light guide plates 14 in the above-described embodiments, thisis not intended to limit the invention. For example, another case may beprovided in the probe body, and the securing member, such as a resin,may be provided between that case and the light guide plates 14 tosecure the light guide plates 14 in the probe body. In the thirdembodiment, the securing member, such as a resin, may be providedbetween another case provided in the probe body and the holding member18 (FIG. 6) to secure the light guide plates 14 in the probe body.

Further, although the light guide plates 14 in the third to sixthembodiments (FIGS. 6 to 9) are disposed obliquely so that light is alsoapplied to an area immediately below the ultrasound transducers 12, itis not necessary to dispose the light guide plates 14 obliquely in theseembodiments. On the other hand, the light guide plates 14 in the firstand second embodiments (FIGS. 2, 5, etc.) may be disposed obliquely.

The above-described embodiments may be combined, as appropriate. Forexample, the third embodiment may be combined with the fourth embodimentsuch that the holding member 18 (FIG. 6) that holds the ultrasoundtransducers 12 is provided in the structure shown in FIG. 7, and thefirst light guide members 141 and the second light guide members 143 ofthe light guide plates 14 a are secured between the case 15 and theholding member 18. The third embodiment may be combined with the fifthembodiment such that the holding member 18 (FIG. 6) that holds theultrasound transducers 12 is provided in the structure shown in FIG. 8,and the second light guide members 143 of the light guide plates 14 aare secured between the case 15 and the holding member 18.

Further, the third embodiment may be combined with the sixth embodimentsuch that the resin 16 covers the light exit ends of the light guideplates 14, as shown in FIG. 9, in the structure shown in FIG. 6. Thefourth embodiment may be combined with the sixth embodiment such thatthe resin 16 covers the light exit ends of the light guide plates 14 a(the light exit ends of the second light guide members 143), as shown inFIG. 9, in the structure shown in FIG. 7. The fifth embodiment may becombined with the sixth embodiment such that the resin 16 covers thelight exit ends of the light guide plates 14 a (the light exit ends ofthe second light guide members 143), as shown in FIG. 9, in thestructure shown in FIG. 8.

Further, the third embodiment, the fourth embodiment and the sixthembodiment may be combined such that, in the structure shown in FIG. 7,the first light guide members 141 and the second light guide members 143of light guide plates 14 a are secured between the case 15 and theholding member 18, and the resin 16 covers the light exit ends of thelight guide plates 14 a (the light exit ends of the second light guidemembers 143), as shown in FIG. 9. The third embodiment, the fifthembodiment and the sixth embodiment may be combined such that, in thestructure shown in FIG. 8, the second light guide members 143 of thelight guide plates 14 a are secured between the case 15 and the holdingmember 18, and the resin 16 covers the light exit ends of the lightguide plates 14 a (the light exit ends of the second light guide members143), as shown in FIG. 9.

The present invention has been described based on the preferredembodiments. However, the probe of the invention is not limited to theprobes of the above-described embodiments, and various modifications andchanges made to the above-described embodiments are also within thescope of the invention.

What is claimed is:
 1. A probe comprising: an acoustic wave detectorthat detects at least an acoustic wave from the subject; an opticalfiber that guides light emitted from a light source to a probe body; anda light guide member that guides light from a light entrance end to alight exit end, the light entrance end being optically coupled to theoptical fiber and the light exit end being located in the vicinity ofthe acoustic wave detector, wherein the light guide member is secured inthe probe body with a securing material provided at least partiallyaround the light guide member, and the conditional expression below issatisfied:sin⁻¹(n2/n1)×(180°/π)<90°−θi where n1 is a refractive index of the lightguide member, n2 is a refractive index of the securing material, and θiis a spread angle of light entering the light entrance end from theoptical fiber.
 2. The probe as claimed in claim 1, wherein the lightguide member is at least partially made of glass.
 3. The probe asclaimed in claim 1, wherein the securing material is made of a fluorineresin material.
 4. The probe as claimed in claim 3, wherein the securingmaterial is made of tetrafluoroethylene-perfluorodioxole copolymer. 5.The probe as claimed in claim 1, wherein the securing material is madeof a fluorosilicone rubber.
 6. The probe as claimed in claim 1, whereinthe securing material is made of a low-refractive index silicone resinor a methyl silicone resin having a refractive index lower than therefractive index of the light guide member.
 7. The probe as claimed inclaim 1, wherein the light exit end of the light guide member is coveredwith the securing material.
 8. The probe as claimed in claim 1, whereinthe light guide member comprises a first light guide member that guideslight emitted from the light source, and a second light guide memberthat diffuses and guides the light guided by the first light guidemember to the vicinity of the acoustic wave detector.
 9. The probe asclaimed in claim 8, wherein the second light guide member comprises alight diffusing member that diffuses incoming light, the light diffusingmember being disposed on the side where light from the first light guidemember enters.
 10. The probe as claimed in claim 9, wherein theconditional expression below is satisfied:sin⁻¹(n2/n3)×(180°/π)<90°−θd, where n3 is a refractive index of thesecond light guide member, θ1 is a diffusion angle of the lightdiffusing member, and θd is (θi²+θ1²)^(1/2).
 11. The probe as claimed inclaim 8, wherein at least the second light guide member of the first andsecond light guide members is secured with the securing material. 12.The probe as claimed in claim 8, wherein only the second light guidemember of the first and second light guide members is secured with thesecuring material.
 13. The probe as claimed in claim 1, wherein thesecuring material is provided to extend over a side surface of the lightguide member between the light entrance end and the light exit end. 14.The probe as claimed in claim 1, wherein the securing material isprovided to extend over a side surface of the light guide member betweenthe light exit end and a position away from the light exit end by apredetermined distance.
 15. The probe as claimed in claim 14, whereinthe predetermined distance is not more than ⅓ of a distance between thelight entrance end and the light exit end.
 16. The probe as claimed inclaim 1, wherein the securing material is provided between the lightguide member and a case forming the probe body or a case provided in theprobe body.
 17. The probe as claimed in claim 1, wherein the light guidemember is secured with the securing member between a case forming theprobe body or a case provided in the probe body and a holding memberthat holds the acoustic wave detector.
 18. The probe as claimed in claim17, wherein the acoustic wave detector is attached to the holding memberafter the light guide member is secured with the securing member.
 19. Aprobe comprising: an acoustic wave detector that detects at least anacoustic wave from the subject; an optical fiber that guides lightemitted from a light source to a probe body; and a light guide memberthat guides light from a light entrance end to a light exit end, thelight entrance end being optically coupled to the optical fiber and thelight exit end being located in the vicinity of the acoustic wavedetector, wherein the light guide member is secured in the probe bodywith a securing material provided at least partially around the lightguide member between the light entrance end and a position away from thelight entrance end by a distance h, wherein h=d/tan (θi), where d is adistance from a position where the optical fiber is coupled to the lightentrance end to a side surface of the light guide member, and θi is aspread angle of light entering the light entrance end from the opticalfiber.
 20. The probe as claimed in claim 19, wherein an area of the sidesurface other than an area corresponding to the distance h from thelight entrance end of the light guide member is covered with a layer ofair.